1. A proposal for a search of galactic axions using magnetized materials
QUAX (QUaerere Axion)
A proposal for a search of galactic axions using magnetized materials
Short theoretical introduction
Current situation
Laboratory searches
The proposal

2. The strong CP problem
The QCD lagrangian contains a term that foresees CP violation
The parameter q is unprescribed by the theory, it is expected to be q ~ 1. QCD interaction actually depends on q through its difference with the phase of the quark mass matrix:
VERY FINE TUNING! -> STRONG CP PROBLEM

3. Dynamical Solution

4. Axion interactions
Several interactions are possible: they are model dependent
Quark
Quark derivative
Gluon A B C
Photon
Lepton D E
Two main models:
Kim-Shifman-Vainstein-Zakharov (KSVZ)
(Kim 1979; Shifman, Vainstein, and Zhakharov 1980)
Dine-Fischler-Srednicki- Zhitnitskii (DFSZ)
(Zhitnitskii 1980; Dine, Fischler, and Srednicki, 1981a, 1981b)

5. Axion interactions 2 Axion interactions are model dependent
Axion photon photon
gg = 0.36 (DFSZ)
gg = (KSVZ)
Axion electron electron
(DFSZ)
ge = 0 (KSVZ)
All couplings are extremely weak!

6. Does the axion exist? Excluded Searches Hint
While the standard Peccei Quinn Weinberg Wilczeck (PQWW) axion was soon ruled out ( Electro Weak Scale F = 250 GeV ), the other axion (DFSZ, KSVZ) continues to evade all current experimental limits
A reduced window of possibilities is actually left for discovery
Excluded
Searches
Hint
From G. Raffelt talk in Vistas in Axion Physics, INT, Seattle, 23–26 April 2012

7. Axions in the galactic halo
In order to explain galaxy rotation curves, an halo of dark matter is hypothesize
Accepted value for local dark matter density
Cold dark matter component is thermalized and has a Maxwellian velocity distribution
There might be a non-thermalized component with sharper velocity distribution

8. Can we detect axions?
Searching for “invisible axion” extremely challenging
Most promising approach to date: use axion-photon-photon vertex
Primakoff effect:
scattering from an electromagnetic field (virtual photon)
In the presence of an external field (magnetic or electric) the axion and the photon mix and give rise to oscillation/conversion
G. Carosi et al, Contemp. Phys. 49, 281 (2008)
Higher magnetic field are easily obtainable than electric fields

9. Haloscopes – Galactic axions
Search for cold dark matter constituent
Original proposal by P. Sikivie (1983)
DM particles converted into photons inside a magnetic field (Primakoff)
The mass of the DM particle determines the frequency of the photons to be detected. For axions we are in the microwave range.
ba~ axion velocity
Use a microwave cavity to enhance signal. Cavity must be tuned to axion mass. Being this unknown, tuning is necessary: very time consuming experiment!
meV <-> GHz

10. Haloscopes – Galactic axions
Search for cold dark matter constituent having galactic density ra
Original proposal by P. Sikivie (1983)
DM particles converted into photons inside a magnetic field (Primakoff)
Expected signal a nearly monochromatic line. Broadened by the thermal distribution of DM in the Milky Way
Power proportional to the number density and the square of the axion-photon coupling

11. Haloscope detectors
Pilot experiments in Brookhaven (1988) and University of Florida (1990)
Second generation experiments:
Lawrence Livermore employing low noise amplifier detectors
Kyoto employing Rydberg atom detectors
ADMX – Axion Dark Matter eXperiment
High Q microwave cavity inside an 8.5 T magnet
Almost Quantum Limited SQUID detector
Reached sensitivity for probing DM axion:
If all galactic DM is all made of axion
If we assume KSVZ model right
If the axion has the right mass, i.e. resonant with the cavity

12. ADMX recent progress and prospects
The experiment goes to a second stage with a collaboration between University of Washington and Yale
New scheme to employ SQUID at higher frequency
New type of amplifier at frequencies above a few Ghz
Use higher order modes in the resonant cavity
Optimize cavity material to obtain higher Qs – hybrid superconducting cavities
Photonic band gap cavity in the multi-GHz range

13. New proposal: QUAX (QUearere AXion)
A new proposal tries to exploit the axion electron coupling
Due to the motion of the solar system in the galaxy, the axion DM cloud acts as an effective magnetic field on electron spin
The ferromagnetic transition in a magnetized sample can be excited and thus emits microwave photons RF
Power
Axion
YIG
Wind
Idea come from several old works:
L.M. Krauss, J. Moody, F. Wilczeck, D.E. Morris, ”Spin coupled axion detections”, HUTP-85/A006 (1985)
L.M. Krauss, ”Axions .. the search continues”, Yale Preprint YTP (1985)
R. Barbieri, M. Cerdonio, G. Fiorentini, S. Vitale, Phys. Lett. B 226, 357 (1989)
A.I. Kakhizde, I. V. Kolokolov, Sov. Phys. JETP (1991)

14. Axion electron interaction
The interaction of the axion with the a spin ½ particle
In the non relativistic approximation
The interaction term has the form of a spin - magnetic field interaction with playing the role of an effective magnetic field

15. Galactic axions
With the following hypothesis:

16. FMR magnetometry
We exploit the Ferromagnetic Resonance (FMR) inside a magnetized ferrimagnetic material
EPR/FMR resonances inside a magnetic media can be tuned by an external magnetizing field and lies in the multi GHz range (radio frequency)
1 T -> 28 GHz

17. Axion RF signal
The axion interaction with the electron spins will excite the FMR transition corresponding to its mass
The emitted power, using the magnetic dipole emission formula, is
M0 – sample magnetization
– spin-spin relaxation time
V – sample volume
w0 = wa – transition angular frequency

18. Axion RF signal Detection noise not a major issue
w0/2p = 17 GHz --> ma=70 meV
Power [Watt]
w0/2p
Frequency [Hz]
Detection noise not a major issue
Commercial low noise HEMT amplifiers have input noise level of ~10-22 W/√Hz

19. Intrinsic noise
Major noise source is magnetization noise: its estimation procedure not well established. We have used two models based on different starting assumptions.
Fluctuation – dissipation theorem: The power spectral density of the magnetization noise is calculated using the imaginary part of the magnetic susceptibility:
Thermal magnon photon emission: the RF emission by the spin waves (magnons) is considered within a RF resonator with quality factor Q (I. Kolokolov)

20. Detection scheme Detection performed in a high Q microwave resonator
Ferrimagnetic material placed in antinodes of the resonator
Resonator in an homogenous axial magnetic field
Cryogenic system to avoid black body photons and to enhance properties of magnetic material
Low noise detector chain (Quantum limited?)
Cavity to enhance SNR

21. QUAX goal
Reach the axion model coupling constant within a 4 year development in a narrow axion mass range
Major issue is to demonstrate that noise sources are under control in reasonable amount of time, thus allowing to extend the mass range in a larger apparatus

22. QUAX Beam Pattern
EFFETTO DIREZIONALE
SPIN ELETTRONE -ASSIONE

23. People PADOVA LEGNARO TORINO TOT FTE INFN 5.3 BIRMINGHAM
Clive Speake Experimentalist - University full professor
MOSCA
Igor Kolokolov - Theoretician - Vice director Landau Institute

24. Activity
1) High Susceptibility Material , Low Dissipation (LNL-INRIM.TO )
2) Low Noise Receiver : Linear / near QL( PD-LNL)
3) High Frequency High Q Microwave Cavity 10^5: (PD-LNL)
4) High Magnetic Field : Tesla ( GE-LNL )
5) 100 milliKelvin ( TN-PD )

25. Peccei Quinn simmetry: the axion
Peccei and Quinn (1977) proposed to solve the strong CP problem by postulating the existence of a global UPQ(1) quasi-symmetry (it is spontaneously broken).
Theta = a(x) /F Campo dinamico
The axion (Weinberg 1978, Wilczeck 1978) is the pseudo Goldstone boson associated with the spontaneous breakdown of the PQ symmetry.
The axion is a light pseudoscalar boson the cousin of the p0 :
mp = 135 MeV – pion mass
fp = 93 MeV – pion decay constant
fa – Peccei Quinn symmetry breaking scale